I am sorry, I do not know the proper Daf that the subject appears on; it may have been a separate dissertation by Rav Yitzchak Hutner on the permissibility of Melacha (as well as the substitute Yomim Tovim when Hallel is said to make up for the 8 Yomim Tovim d'oraisa on which we do not say Hallel).
My question pertains to a reference in the dissertation stating "..Yom Kipur is the day of the greatest Simcha (Megilah, 26b). I looked for the latter reference in Megilah but could not find it and wonder if the Daf given is a typographic error. My interest in the what the Gemorah has to say on that matter stems from my confusion as follows: In the paragraph beginning with "Besides the eight days..." -- it states that Purim is a make-up for the lack of seudah and SIMCHA, which tends to contracdict what is stated two sentences later - "Yom Kippur is the day of the greatest Simchah."
Hence, I would appreciate if you could reconcile the two statements. Perhaps the Simcha on Yom Kipur is sourced in the historical events that took place on Yom Kipur subsequent to Matan Torah? (For example, Melech Shlomo suspended the fast of Yom Kipur at the dedication of the 1st temple and, if I am not mistaken, it was the practice of the Bnos Yisroel to most modestly attract young men to marriage during the solemn day of Yom Kippur)
Thus I would appreciate your respected comment on this along with a confirmation as to where I should look in Megilah.
The Gemara that you quote us having quoting is in Ta'anis 26b, not in Megilah. We looked in our archives for the Insights to Megilah 5b, where the piece which you quote was written, and indeed it says Ta'anis 26b. There, it says that Yom Kipur is the greatest "Yom Tov," which means that it is a day of the greatest Simchah. The reason is because it was on that day that we received the Torah.
Regarding the contradiction that you raised in the Insights, the first sentence should read, "lacking a Se'udah and an expression of Simchah," instead of "lacking a Se'udah and Simchah." The point is that Yom Kipur is indeed the day of great Simchah, and yet there is no expression of that Simchah through eating and drinking. The Simchah of Yom Kipur is that of the Nefesh, and we make up for the lack of expression of the Simchah in a physical way by celebrating on Purim.